Verbal scales: Better than nothing but worse than line scales
How much more is "like extremely" than "like very much" and how much less is "dislike moderately" compared to "dislike slightly"?
Sensory research tries to measure human perception as precisely as possible. This task can only be solved at this point by using human subjects as measuring tools. Only human testers can judge confidently what human consumers will like or dislike. To be able to quantify the subjective impressions of test subjects, different kinds of scales are used. Most often these are based on either 7 or 9 different verbal expressions covering all grades from dislike (rather bad, bad, very bad, extremely bad) on the one end to like (rather good, good...) on the other. It is assumed that every test person using the scale will have the same concept as to the correct order of these expressions, and that the conceptual "distance" from one expression to the next will be perceived to be about equal.
These assumptions were questioned in two experiments conducted by the German Association for Sensory Analysis and Product Development (Ltd), ASAP.
First the ASAP researchers had their subjects freely order the expressions on a magnetic board in the way they personally understood them. The surprising result was that only 30% of the subjects used the scales as had been assumed they would, and chose the experimenter's correct order and equal distances between the expressions. A majority of 70% either changed the order of the expressions and/or chose very different distances between them.
In a second experiment the subjects were asked to rate their subjective impressions first on the traditional 9 point verbal scale and then - in another session - also on a continuous line-scale with only two anchor points (good and bad) near the two ends of the line. This experiment resulted in the same ranking order, which led ASAP researchers to conclude that results evaluated by a verbal scale can be successfully compared and transformed to the use of continuous line scales. Typical difficulties that occur when verbal scales are translated into other languages can thus be prevented. "The great advantage of the use of continuous line scales is that this method gives much finer results which are not "pre-shaped" and possibly "distorted" by a different understanding of the words used", say the scientists. Another advantage they sight is that the ratings made on line scales can be very easily converted into numbers by computer software. This helps to get easier and cheaper data that is less prone to errors than data transferred by hand. "We therefore suggest using nonverbal scaling methods in sensory research whenever possible," concludes ASAP director Kurt Benz.
ASAP GmbH, Association for Sensory Analysis and Product Development, Munich, Germany
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